Looking back at La Nina's impacts

On Thursday, La Nina was officially declared to be over by the National Oceanic Atmospheric Administration (NOAA). Unfortunately, when it is reported to the public that La Nina (or its counterpart El Nino) are either coming or going, the impacts are often way too generalized. While it's natural to desire explanations that are set in stone for what these two climate phenomena will cause in the United States, it's just not that simple.

Senior Meteorologist Stu Ostro (Find him on Facebook | Twitter) reinforces the point, “I am driven to distraction by the way El Nino and La Nina are sometimes described by the press and even scientists. That they’re the be-all-end-all of everything, and when either one begins or ends, that always and absolutely equates to a particular weather outcome. It’s not that black-and-white!”

When the information came in last fall that a new La Nina was taking shape, the reports for Texas were dire since they were in a multibillion-dollar drought disaster and La Nina typically (notice I said typically) brings drier-than-average conditions to the Lone Star State.

While La Nina did contribute to the intensifying drought over the previous winter (2010-2011), it was not the case this past winter.

In fact, it was the 14th wettest December through February period on record in Texas! This was followed by the 8th wettest March on record. The percentage of the state in exceptional drought (worst category) has fallen from 88 percent in early October to 8 percent in early May.

Two separate La Nina winters and two different outcomes.

Below-average temperatures during the winter months are another aspect of La Nina's influence that we look for across a large amount of real estate from Washington and Oregon eastward to Idaho, Montana, Wyoming and the Dakotas.

Not so much in the winter of 2011-2012.

The December through February period turned out to be among the top fifteen warmest for Montana, North Dakota and South Dakota. Temperatures finished near average in both Washington and Oregon during this same timeframe, despite a colder-than-average December.

La Nina winters also typically bring wetter-than-average conditions to western Washington and western Oregon. While March was among the wettest on record for these states, the December through February timeframe was the 10th driest on record in Oregon and the 25th driest on record in Washington.

So, where exactly might we have seen La Nina's thumbprint this past winter now that we've shown a couple of examples of where it didn't?

From Texas, La Nina typically brings drier-than average conditions to the immediate Gulf Coast eastward to south Georgia and Florida. As we emerged from winter into spring, this is where drought conditions had grown considerably.

In late November, only 26 percent of the Sunshine State was in drought (northern Florida). As of May 1, this figure is now at 89 percent. Only far south Florida is not experiencing drought conditions.

It's a similar story in Georgia, where drought conditions expanded significantly during the winter. Almost all of southern and central Georgia is in extreme or exceptional drought (two worst categories).

Here's one more example.

Much of the country east of the Rockies experienced a winter with well above-average temperatures, propelling the United States to its fourth warmest winter on record. This included the swath from the Mid-Atlantic to the South, which typically sees warmer-than-average temperatures during La Nina winters.

Ironically, it's this same geographical region that actually saw well below-average temperatures the previous winter when La Nina conditions were also present.

As you can see, not all La Ninas/El Ninos are created the same. There can be other overriding factors in the atmosphere that can mute out or enhance certain aspects of what we typically expect from these climate influences.